The present invention generally relates to bidirectional power converters and more particularly to such power converters which may convert power at low power rates and high power rates up to 10 Kilowatts (KW) or more.
Recent advancements in electric renewable energy sources and storage systems like fuel cells, batteries and super capacitors, and increased demand for transportation equipment with increased electrical power requirements have resulted in a need for light weight and efficient power electronic converters. Because of reliability and other technical issues, optimal voltages for batteries and super capacitors are relatively low. On the other hand, for efficient power transmission (low I2R losses) between source and load these low voltages may need to be converted to higher values on a high voltage DC bus. The power flow may also be reversed in regenerative operations and also when batteries and super capacitors are charged. These issues are typically addressed with bidirectional DC to DC converters.
To have a compact and light weight converter, its operating frequency should be high so that the size of magnetics and capacitors can be reduced for the same amount of power. Also, the efficiency of the converter should be high not only for the sake of low energy losses, but also to reduce the size of cooling components which affect overall size and weight of the converters.
Operating at high switching frequency (e.g., above 100 KHz) may require soft switching techniques. In soft switching, a switching device may be switched (turned on or off) when the device has a zero voltage (zero voltage switching, ZVS) or zero current (zero current switching, ZCS). In frequencies above 20 KHz, switching losses are usually dominant causes of losses in switching devices, whereas below that frequency, conduction losses are dominant. Soft switching may also preclude damage to high frequency switching devices which may otherwise result from excessive internal switching losses at high frequencies even in no load conditions.
As can be seen, there is a need for a bidirectional converter which can operate with soft switching at high frequencies (e.g., 100 KHz or higher) and at high power levels (e.g., up to 10 KW) while performing with high efficiency. Additionally there is a need for such a power converter that may operate with soft switching even at low power levels.